" 19."cos A+cos(120^(@)-A)+cos(120^(@)+A)=0

cosA+cos(120^(@)-A)+cos(120^(@)+A)=0

cosA+cos(120^(@)-A)+cos(120^(@)+A)=0

cos120^(@)=

Prove the following: (i) "sin" alpha+"sin"(alpha+(2pi)/(3))+"sin"(alpha+(4pi)/(3))=0 (ii) cos A+cos(120^(@)-A)+cos(120^(@)+A)=0 .

Prove that (i) sin A+sin (120^(@)+A)+sin(240^(@)+A)=0 (ii) cos A+cos (120^(@)+A)+cos (120^(@)-A)=0

Prove the following : cos A + cos (120^@ - A) + cos (120^@+ A) = 0 .

" cos x + cos " (120^(@) -x ) + " cos "(120^(@) +x)=0

cos (120^(@)) is -

cos A + cos ( 120 ^@+A ) + cos ( 120^@ -A ) is

The period of cosx cos (120^(0) - x) cos (120^(0) + x) is